There has been already known to externally add to the developing agent a substance for controlling the electrostatic charge amount of a dry magnetic one-component developer, i.e., dry silica.
It is widely known in the art that a developing apparatus using such a developer, when used, for example, in a thin developer layer form formed on a sleeve to develop a latent image, provides an image having an increased image density and being free from roughness, in comparison with a case where a latent image is developed using a developer without external addition of silica.
Various developing devices have already been proposed for maintaining superior developing characteristics of the developer.
For example, JP-A-63-311367 (The term "JP-A" as used herein means an "unexamined published Japanese patent application) discloses a developer carrier having thereon a resin layer having a resistance of from 10.sup.9 to 10.sup.13 .OMEGA..cndot.cm. Further, JP-A-4-166864 discloses a developer carrier comprising graphite and positive-charged resin particles. Furthermore, JP-A-4-246676 discloses a developer carrier having specific surface roughness regulated by surface abrasion treatment.
JP-A-6-289697 discloses a developing apparatus in which a vibrating electric field is applied to a layer-thickness regulating member for a developer.
However, the developer carrier disclosed in JP-A-63-311367 has a high surface resistance and thus tends to cause development ghosts, which correspond to hysteresis of a printed pattern, on the developer carrier in the case, for example, where a developer having externally added a negative silica which is enduring for use in a negative developer.
In the developer carrier disclosed in JP-A-4-166864, the content of the positive-charged resin particles is limited, so that the positive-charged resin particles tends to be unevenly dispersed. Consequently, the resistance of a surface coating layer formed of the positive-charged resin particles becomes uneven, thereby easily causing leaks or development ghosts.
In the developer carrier disclosed in JP-A-4-246676, the developer surface becomes smooth by the surface abrasion treatment. As a result, the transfer amount of a developer is reduced, thereby resulting in a reduction in image density.
Further, in the developing apparatus disclosed in JP-A-6-289697, a vibrating electric field is applied to act on the layer-thickness regulating member for a developer layer for inhibiting reduction in image density, fogging of non-image areas and development ghosts. However, this technique is fundamentally technically disadvantageous because it arise an increase in costs resulting from the necessity of provision of an equipment for applying a vibrating electric field.